It is known that aryl halides can be converted into aromatic nitrites using alkali metal cyanides in the presence of catalysts, for example nickel complexes. Adv. in Chem. Series 132: Homogeneous Catalysis II, 252-273 (1974) describes the nickel-catalysed cyanation of aryl halides with alkali metal cyanides in detail. The catalysts used were Ni(0) or Ni(II) complexes having generally mono- or bidentate arylphosphine ligands. The solvents used were alcohols, such as methanol and ethanol, and dipolar-aprotic solvents, such as dimethylformamide. It is only possible to carry out the reaction with good yields if the concentration of the cyanide ions is controlled exactly. Acetone has been employed as solvent only for the cyanation of unsubstituted chlorobenzene. Here, a selectivity of 82% was achieved, at a conversion of 58%, and 10% of an undesired coupling product (biphenyl) were obtained. For a process that is to be carried out on an industrial scale, these are very unfavourable values. Later, it was found that the catalyst is cyanated irreversibly at higher cyanide concentrations see Bull. Chem. Soc. Jpn. 61, 1985 (1988) and J. Organomet. Chem. 173, 335 (1979)).
EP-A 384 392 describes the cyanation of optionally halogen-, formyl- or trifluoro-methyl-substituted chloro- or bromobenzene in the presence of catalysts prepared in situ from nickel chloride. The reaction is carried out in anhydrous lower alcohols or dipolar aprotic solvents. Here, the yields are frequently unsatisfactory. In many cases, a further disadvantage is dehalogenation, which proceeds as a side reaction. The preferred solvent--acetonitrile owing to its toxicity and tetrahydrofuran owing to its tendency to form peroxides--can be handled on an industrial scale only with great expense.
For 2-thio-3-amino-chlorobenzene, WO 96/11906 describes the cyanation in the presence of phosphine nickel catalysts in aprotic polar solvents. Not to mention the specific substitution pattern of the substrate, the 11-22 mol % of tetrakis-triphenylphosphine-nickel constitute uneconomically high amounts of catalyst. EP-A 613 720 likewise describes a process for preparing aromatic nitriles in which the preferred solvent employed is tetrahydrofuran, which has the above-mentioned disadvantages.